U.S. patent number 6,768,529 [Application Number 09/748,212] was granted by the patent office on 2004-07-27 for reflection-transmission double type liquid-crystal display device.
This patent grant is currently assigned to Nitto Denko Corporation. Invention is credited to Hideo Abe, Toshihiko Ariyoshi, Seiji Umemoto.
United States Patent |
6,768,529 |
Umemoto , et al. |
July 27, 2004 |
Reflection-transmission double type liquid-crystal display
device
Abstract
A reflection-transmission double type liquid-crystal display
device has a transmission type liquid-crystal display panel
including a liquid-crystal cell, at least one illuminator disposed
on at least one side surface of the liquid-crystal display panel,
an optical path changing sheet which has a refractive index
exhibiting a refractive index difference of not higher than 0.15
from a refractive index of a nearest liquid-crystal cell substrate
and is bonded onto a back side of the liquid-crystal display panel
through an adhesive layer having a refractive index exhibiting a
refractive index difference of not higher than 0.20 from the
refractive index of the nearest liquid-crystal cell substrate, and
a reflection layer disposed on a back side of the optical path
changing sheet. The optical path changing sheet includes optical
path changing slopes and flat surfaces. Each of the optical path
changing slopes faces the illuminator at an inclination angle in a
range of from 30 to 48 degrees with respect to a plane of the
optical path changing sheet and being provided for reflecting
incident light from the illuminator toward the visual side of the
liquid-crystal display panel. Each of the flat surfaces is inclined
at an inclination angle of not larger than 10 degrees with respect
to the sheet plane, and a projected area of the flat surfaces on
the sheet plane is not smaller than 10 times as large as a
projected area of the optical path changing slopes.
Inventors: |
Umemoto; Seiji (Osaka,
JP), Ariyoshi; Toshihiko (Osaka, JP), Abe;
Hideo (Osaka, JP) |
Assignee: |
Nitto Denko Corporation (Osaka,
JP)
|
Family
ID: |
18495136 |
Appl.
No.: |
09/748,212 |
Filed: |
December 27, 2000 |
Foreign Application Priority Data
|
|
|
|
|
Dec 27, 1999 [JP] |
|
|
P. 11-369712 |
|
Current U.S.
Class: |
349/114;
349/67 |
Current CPC
Class: |
G02B
6/0061 (20130101); G02F 1/133615 (20130101); G02F
1/133616 (20210101); G02B 6/0038 (20130101); G02B
6/0036 (20130101); G02F 2203/02 (20130101) |
Current International
Class: |
F21V
8/00 (20060101); G02F 1/1335 (20060101); G02F
1/13 (20060101); G02F 001/133 () |
Field of
Search: |
;349/113-114,61,64-65,112 ;362/26-30 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
0 957 392 |
|
Nov 1999 |
|
EP |
|
5-158033 |
|
Jun 1993 |
|
JP |
|
11-142618 |
|
May 1998 |
|
JP |
|
2000-147499 |
|
May 2000 |
|
JP |
|
Other References
Patent Abstracts of Japan, vol. 1996, No. 08, Aug. 30, 1996 &
JP 08 094844 A (Fujitsu Ltd), Apr. 12, 1996 (abstract)..
|
Primary Examiner: Nguyen; Dung
Attorney, Agent or Firm: Sughrue Mion, PLLC
Claims
What is claimed is:
1. A reflection-transmission double type liquid-crystal display
device comprising: a transmission type liquid-crystal display panel
including a liquid-crystal cell; at least one illuminator disposed
on at least one of side surfaces of said liquid-crystal display
panel and capable of being switched on/off; an optical path
changing sheet which has a refractive index exhibiting a refractive
index difference of not higher than 0.15 from a refractive index of
a nearest liquid-crystal cell substrate, and which is bonded onto a
back side opposite to a visual side of said liquid-crystal display
panel through an adhesive layer having a refractive index
exhibiting a refractive index difference of not higher than 0.20
from the refractive index of said nearest liquid-crystal cell
substrate; and a reflection layer disposed on a back side of said
optical path changing sheet, wherein said optical path changing
sheet has continuous first optical path changing slopes, second
optical path changing slopes and flat surfaces, each of said first
optical path changing slopes faces said illuminator at an
inclination angle in a range of from 30 to 48 degrees with respect
to a plane of said optical path changing sheet for reflecting
incident light from said illuminator toward said visual side of
said liquid-crystal display panel, each of said second optical path
changing slopes faces away from said illuminator at an inclination
angle which is less than 90 degrees with respect to a plane of said
optical path changing sheet and is greater than said inclination
angle of said first optical path changing slopes, and each of said
flat surfaces is inclined at an inclination angle of not larger
than 10 degrees with respect to said sheet plane so that a
projected area of said flat surfaces on said sheet plane is not
smaller than 10 times as large as a projected area of said first
optical path changing slopes on said sheet plane.
2. A reflection-transmission double type liquid-crystal display
device according to claim 1, wherein said liquid-crystal display
panel further includes a polarizer disposed on one or each of side
surfaces of said liquid-crystal cell.
3. A reflection-transmission double type liquid-crystal display
device according to claim 2, wherein said liquid-crystal display
panel further includes at least one phase retarder disposed between
said liquid-crystal cell and said polarizer.
4. A reflection-transmission double type liquid-crystal display
device according to claim 1, wherein each of cell substrates for
said liquid-crystal cell is made of an optically isotropic
material.
5. A reflection-transmission double type liquid-crystal display
device according to claim 1, wherein said first optical path
changing slopes are inclined at an angle of not larger than 30
degrees with respect to said side surface on which said illuminator
is disposed; and said optical path changing sheet is disposed so
that said optical-path-changing-slope-forming surface of said
optical path changing sheet is located on said back side of said
optical path changing sheet.
6. A reflection-transmission double type liquid-crystal display
device according to claim 1, wherein a refractive index difference
between said adhesive layer and said nearest liquid-crystal cell
substrate and between said optical path changing sheet and said
nearest liquid-crystal cell substrate is not larger than 0.10.
7. A reflection-transmission double type liquid-crystal display
device according to claim 1, wherein said first optical path
changing slopes inclined at an inclination angle of from 35 to 46
degrees with respect to said sheet plane.
8. A reflection-transmission double type liquid-crystal display
device according to claim 7, wherein each of said prismatic
structures of said optical path changing sheet is constituted by a
concave portion substantially shaped like a triangle in
section.
9. A reflection-transmission double type liquid-crystal display
device according to claim 7, wherein said prism-like concave
portions are constituted by continuous grooves extended from one
end of said optical path changing sheet to the other end thereof in
a ridgeline direction parallel to or inclined to said side surface
of said liquid-crystal display panel on which said illuminator is
disposed.
10. A reflection-transmission double type liquid-crystal display
device according to claim 1, wherein light reflected by said
reflection layer is diffused so as to be made incident on said
liquid-crystal cell.
11. A reflection-transmission double type liquid-crystal display
device according to claim 10, wherein at least said reflection
layer, said optical path changing sheet or said adhesive layer for
bonding said reflection layer to said liquid-crystal display panel
exhibits light diffusing characteristic.
12. A reflection-transmission double type liquid-crystal display
device according to claim 11, wherein said light diffusion type
reflection layer has a rough surface of fine prismatic structures,
and a high-reflectance metal thin film disposed on said rough
surface of fine prismatic structures, or wherein a light diffusing
layer is disposed on an optical-path-changing-sheet-side surface of
said high-reflectance metal thin film.
13. A reflection-transmission double type liquid-crystal display
device according to claim 11, wherein said reflection layer
comprises a high-reflectance metal thin film which is provided onto
an optical-path-changing-slope-forming surface of said optical path
changing sheet, the optical-path-changing-slope-forming surface
being roughened, or onto an optical-path-changing-slope-forming
surface of a light diffusion type optical path changing sheet; or
wherein said reflection layer comprises a high-reflectance metal
thin film which is provided onto an
optical-path-changing-slope-forming surface of said optical path
changing sheet, said optical path changing sheet being bonded
through a light diffusion type adhesive layer.
14. A reflection-transmission double type liquid-crystal display
device comprising: a transmission type liquid-crystal display panel
including a liquid-crystal cell; at least one illuminator disposed
on at least one of side surfaces of said liquid-crystal display
panel and capable of being switched on/off; an optical path
changing sheet which has a refractive index exhibiting a refractive
index difference of not higher than 0.15 from a refractive index of
a nearest liquid-crystal cell substrate, and which is bonded onto a
back side opposite to a visual side of said liquid-crystal display
panel through an adhesive layer having a refractive index
exhibiting a refractive index difference of not higher than 0.20
from the refractive index of said nearest liquid-crystal cell
substrate; and a reflection layer disposed on a back side of said
optical path changing sheet, wherein said optical path changing
sheet has optical path changing slopes and flat surfaces, each of
said optical path changing slopes faces said illuminator at an
inclination angle in a range of from 30 to 48 degrees with respect
to a plane of said optical path changing sheet for reflecting
incident light from said illuminator toward said visual side of
said liquid-crystal display panel, and each of said flat surfaces
is inclined at an inclination angle of not larger than 10 degrees
with respect to said sheet plane so that a projected area of said
flat surfaces on said sheet plane is not smaller than 10 times as
large as a projected area of said optical path changing slopes on
said sheet plane, wherein said optical path changing sheet includes
a repetitive structure of prismatic structures having optical path
changing slopes inclined at an inclination angle of from 35 to 46
degrees with respect to said sheet plane, wherein said prism-like
concave portions are constituted by discontinuous grooves each of
which has a length of not smaller than 5 times as large as a depth
of said groove and in which a longitudinal direction of said groove
is substantially parallel to said side surface of said
liquid-crystal display panel on which said illuminator is
disposed.
15. A reflection-transmission double type liquid-crystal display
device comprising: a transmission type liquid-crystal display panel
including a liquid-crystal cell; at least one illuminator disposed
on at least one of side surfaces of said liquid-crystal display
panel and capable of being switched on/off; an optical path
changing sheet which has a refractive index exhibiting a refractive
index difference of not higher than 0.15 from a refractive index of
a nearest liquid-crystal cell substrate, and which is bonded onto a
back side opposite to a visual side of said liquid-crystal display
panel through an adhesive layer having a refractive index
exhibiting a refractive index difference of not higher than 0.20
from the refractive index of said nearest liquid-crystal cell
substrate; and a reflection layer disposed on a back side of said
optical path changing sheet, wherein said optical path changing
includes a plurality of continuous and adjacent, first and second
optical path changing slopes, each of said first optical path
changing slopes faces said illuminator at an inclination angle in a
range of from 30 to 48 degrees with respect to a plane of said
optical path changing sheet for reflecting incident light from said
illuminator toward said visual side of said liquid-crystal display
panel, each of said second optical path changing slopes faces away
from said illuminator at an inclination angle of not larger than 10
degrees with respect to said sheet plane so that a projected area
of said second optical path changing slopes on said sheet plane is
not smaller than 10 times as large as a projected area of said
first optical path changing slopes on said sheet plane.
16. A reflection-transmission double type liquid-crystal display
device comprising: a transmission type liquid-crystal display panel
including a liquid-crystal cell; at least one illuminator disposed
on at least one of side surfaces of said liquid-crystal display
panel and capable of being switched on/off; an optical path
changing sheet which has a refractive index exhibiting a refractive
index difference of not higher than 0.15 from a refractive index of
a nearest liquid-crystal cell substrate, and which is bonded onto a
back side opposite to a visual side of said liquid-crystal display
panel through an adhesive layer having a refractive index
exhibiting a refractive index difference of not higher than 0.20
from the refractive index of said nearest liquid-crystal cell
substrate; and a reflection layer disposed on a back side of said
optical path changing sheet, wherein said optical path changing
sheet has a plurality of optical path changing means having a
concave shape formed by first and second optical path changing
slopes and flat surfaces interposed between said first and second
optical path changing slopes, each of said first optical path
changing slopes faces said illuminator at an inclination angle in a
range of from 30 to 48 degrees with respect to a plane of said
optical path changing sheet for reflecting incident light from said
illuminator toward said visual side of said liquid-crystal display
panel, each of said second optical path changing slopes faces away
from said illuminator, and each of said flat surfaces is inclined
at an inclination angle of not larger than 10 degrees with respect
to said sheet plane.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transmission-reflection double
type liquid crystal display device which can be reduced in
thickness and weight easily and which is excellent in display
quality.
The present application is based on Japanese Patent Application No.
Hei. 11-369712, which is incorporated herein by reference.
2. Description of the Related Art
A liquid-crystal display device in which a back-lighting system
using a bottom-lighting type or side-lighting type light pipe is
disposed on a back side (opposite to a visual side) of a
transmission type liquid-crystal display panel through a
half-transmission type reflector is heretofore known as a
reflection-transmission double type liquid-crystal display device
which can be viewed in a transmission mode by using a built-in
illuminator in addition to a reflection mode by using external
light. The half-transmission type reflector is disposed in order to
enable viewing in a reflection mode. If there is no
half-transmission type reflector, viewing in a reflection mode by
using external light is so dark that the liquid-crystal display
device substantially hardly functions as a reflection type
liquid-crystal display device.
The background-art reflection-transmission double type
liquid-crystal display device using a back-lighting system,
however, has the following problem. That is, it is difficult to
reduce the thickness, size and weight of the liquid-crystal display
device though greater reduction in thickness, size and weight of
the liquid-crystal display device has been demanded for the purpose
of reducing in size and weight of a portable telephone set, a
portable personal computer, or the like. Incidentally, in a
bottom-lighting type back-lighting system, a thickness of not
smaller than 4 mm is generally required for a light diffusing plate
and a reflector which are disposed together with the illuminator.
In a side-lighting type light pipe, a plate thickness of not
smaller than 1 mm is required for light transmission. If a light
diffusing plate, a reflector, a prism sheet, etc. are further
disposed on the side-lighting type light pipe, a further thickness
of not smaller than 3 mm is generally required. If at least one
half-transmission type reflector is still further added, the volume
and weight of the liquid-crystal display device become even larger.
Moreover, there is a problem that viewing in a transmission mode
becomes dark because of the arrangement of the half-transmission
type reflector and that brightness in a reflection mode is inferior
to that of a reflection exclusive type liquid-crystal display
device using a high-reflectance reflection layer.
SUMMARY OF THE INVENTION
An object of the present invention is to develop a
transmission-reflection double type liquid-crystal display device
which can be reduced in thickness and weight easily and which is
excellent in display quality.
According to the present invention, there is provided a
reflection-transmission double type liquid-crystal display device
comprising: a transmission type liquid-crystal display panel
including a liquid-crystal cell; at least one illuminator disposed
on at least one of side surfaces of the liquid-crystal display
panel and capable of being switched on/off; an optical path
changing sheet which has a refractive index exhibiting a refractive
index difference of not higher than 0.15 from a refractive index of
a nearest liquid-crystal cell substrate, and which is bonded onto a
back side (opposite to a visual side) of the liquid-crystal display
panel through an adhesive layer having a refractive index
exhibiting a refractive index difference of not higher than 0.20
from the refractive index of the nearest liquid-crystal cell
substrate; and a reflection layer disposed on a back side of the
optical path changing sheet; the optical path changing sheet
including optical path changing slopes and flat surfaces, each of
the optical path changing slopes facing the illuminator at an
inclination angle in a range of from 30 to 48 degrees with respect
to a plane of the optical path changing sheet and being provided
for reflecting incident light from the illuminator toward the
visual side of the liquid-crystal display panel, each of the flat
surfaces being inclined at an inclination angle of not larger than
10 degrees with respect to the sheet plane so that a projected area
of the flat surfaces on the sheet plane is not smaller than 10
times as large as a projected area of the optical path changing
slopes on the sheet plane.
According to the present invention, while incident light from an
illuminator disposed on one of side surfaces of a liquid-crystal
display panel is transmitted backward efficiently by use of
liquid-crystal cell substrates, the optical path of the
transmission light is changed efficiently toward the visual side of
the liquid-crystal display panel through an optical path changing
sheet disposed on the back side of the panel. Hence, the
transmission light can be utilized for liquid-crystal display in a
transmission mode. Moreover, external light can be
transmitted/reflected efficiently through/by flat surfaces of the
optical path changing sheet and a reflection layer. Hence, the
external light can be utilized for liquid-crystal display in a
reflection mode. The illuminator which is disposed on the side
surface, the optical path changing sheet which is excellent in
thickness, and the reflection layer can form a back-lighting
(transmission mode) system and a reflection mode system. Hence, a
transmission-reflection double type liquid-crystal display device
which is excellent in thickness and light in weight, and which is
bright and excellent in display quality can be formed.
The aforementioned effect is based mainly on use of a slope
reflection type optical path changing sheet. That is, light
incident on a side surface or transmission light of the incident
light is reflected by slopes of the optical path changing sheet so
that the optical path of the light can be changed with good
directivity. Hence, good visibility in a transmission mode can be
achieved. Moreover, external light is transmitted through flat
surfaces of the optical path changing sheet so that the external
light can be kept sufficiently. Hence, good visibility in a
reflection mode can be also achieved. In a method of scatter
reflection by a roughened surface, it is difficult to achieve the
aforementioned effect. Incidentally, JP-A-5-158033 discloses a
reflection type liquid-crystal display device in which illumination
light is made incident on one of side surfaces of a liquid-crystal
display panel and totally reflected by a visual side cell substrate
and in which the reflected light is scattered by a rough surface
type reflector so that the scattered light is utilized for
display.
In the aforementioned case, however, light allowed to be utilized
for display is light that comes out from the panel due to coming
contrary against the total reflection condition by scattering.
Generally, scattered light exhibits a normal distribution having a
direction of regular reflection as a peak, in Extended Abstracts
(20th Liquid-Crystal Discussion Lecture Vol. 3 G510, Tohoku
University; Uchida et al). Hence, the aforementioned display light
is light largely inclined with respect to a frontal (vertical)
direction and therefore hardly utilized effectively for display.
Hence, the display becomes dark in the frontal direction.
Nevertheless, intensifying scattering by the roughened surface type
reflector is unfavorable to display in a reflection mode because
the quantity of light in the frontal direction in the reflection
mode is reduced (SID 96 DIGEST pp.149-152). It is, therefore,
necessary to adjust scattering intensity to keep balance between
both transmission and reflection modes in such a roughened surface
type scattering reflection method. It is, however, difficult to
obtain scattering intensity favorable to the two reflection and
transmission modes because scattering intensity required in the
transmission mode is antinomic to scattering intensity required in
the reflection mode.
On the other hand, the slope reflection type optical path changing
sheet according to the present invention mainly utilizes light
exhibiting a peak in a direction of regular reflection and controls
the optical path of the reflected light. Hence, directivity,
especially frontal directivity, favorable to display can be
provided easily, and a bright transmission mode can be achieved.
Also in a reflection mode, flat portions of the optical path
changing sheet except the slopes can be utilized, and efficient
entrance, reflection and transmission of external light can be
ensured. Hence, the state of light can be balanced easily so as to
be favorable to both transmission and reflection modes.
Features and advantages of the invention will become understood
from the following detailed description of the preferred
embodiments described in conjunction with the attached
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is an explanatory sectional view showing an example of a
reflection-transmission double type liquid-crystal display
device;
FIG. 2 is an explanatory sectional view showing another example of
the reflection-transmission double type liquid-crystal display
device;
FIG. 3 is an explanatory sectional view showing a further example
of the reflection-transmission double type liquid-crystal display
device;
FIGS. 4A, 4B, 4C, 4D, 4E, 4F, and 4G are explanatory side views
showing various optical path changing means in an optical path
changing sheet;
FIG. 5 is an explanatory perspective view showing a further example
of the reflection-transmission double type liquid-crystal display
device;
FIG. 6 is an explanatory perspective view showing a further example
of the reflection-transmission double type liquid-crystal display
device;
FIG. 7 is an explanatory perspective view showing a further example
of the reflection-transmission double type liquid-crystal display
device;
FIG. 8 is an explanatory side view showing an example of the
optical path changing sheet; and
FIG. 9 is an explanatory side view showing another example of the
optical path changing sheet.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The reflection-transmission double type liquid-crystal display
device according to the present invention comprises: a transmission
type liquid-crystal display panel including a liquid-crystal cell;
at least one illuminator disposed on at least one of side surfaces
of the liquid-crystal display panel and capable of being switched
on/off; an optical path changing sheet which has a refractive index
exhibiting a refractive index difference of not higher than 0.15
from a refractive index of a nearest liquid-crystal cell substrate,
and which is bonded onto a backside (opposite to a visual side) of
the liquid-crystal display panel through an adhesive layer having a
refractive index exhibiting a refractive index difference of not
higher than 0.20 from the refractive index of the nearest
liquid-crystal cell substrate; and a reflection layer disposed on a
back side of the optical path changing sheet; the optical path
changing sheet including optical path changing slopes and flat
surfaces, each of the optical path changing slopes facing the
illuminator at an inclination angle in a range of from 30 to 48
degrees with respect to a plane of the optical path changing sheet
and being provided for reflecting incident light from the
illuminator toward the visual side of the liquid-crystal display
panel, each of the flat surfaces being inclined at an inclination
angle of not larger than 10 degrees with respect to the sheet plane
so that a projected area of the flat surfaces on the sheet plane is
not smaller than 10 times as large as a projected area of the
optical path changing slopes on the sheet plane. FIGS. 1 to 3 show
examples of the liquid-crystal display device. In FIGS. 1 to 3, L
designates a liquid-crystal display panel; 11, an optical path
changing sheet; A1, an optical path changing slope; A2 and A3, flat
surfaces; 81, a reflection layer; and 91 and 93, illuminators.
A suitable transmission type display panel at least having a
liquid-crystal cell may be used as the liquid-crystal display panel
L. That is, as shown in FIGS. 1 to 3, a display panel has at least
a liquid-crystal cell. The liquid-crystal cell has liquid crystal
70 enclosed by cell substrates 41 and 42 through a sealing material
71. Thus, the light incident on a side of arrangement of the
optical path changing sheet 11 is made to go out as display light
from the other side of the arrangement through control by means of
the liquid crystal. The liquid-crystal display panel L is not
particularly limited in kind.
Incidentally, on the basis of the format of alignment of liquid
crystal, specific examples of the liquid-crystal cell include a TN
liquid-crystal cell, an STN liquid-crystal cell, a perpendicularly
aligned cell, an HAN cell, a twisted or non-twisted cell such as an
OCB cell, a guest-host liquid-crystal cell, a ferroelectric
liquid-crystal cell, etc. Further, a suitable drive method such as
an active matrix method or a passive matrix method may be used as
the method for driving liquid crystal. As shown in FIGS. 1 to 3,
the liquid crystal is generally driven through transparent
electrodes 51 and 52 provided on the inner surfaces of the pair of
cell substrates 41 and 42.
A suitable transparent substrate such as a glass substrate or a
resin substrate can be used as each of the cell substrates.
Especially, a substrate made of an optically isotropic material is
preferably used from the point of view of display quality, etc. A
substrate such as a non-alkali glass plate exhibiting excellent
colorlessness and transparency with respect to a blue glass plate
is preferably used from the point of view of improvement of
luminance and display quality, etc. A resin substrate is preferably
used from the point of view of reduction in weight, etc. The
thickness of the cell substrate can be determined suitably in
accordance with enclosing strength of liquid crystal, or the like,
without any particular limitation. The thickness of the cell
substrate is generally selected to be in a range of from 10 .mu.m
to 5 mm, particularly in a range of from 50 .mu.m to 2 mm, more
particularly in a range of from 100 .mu.m to 1 mm, from the point
of view of balance between light transmission efficiency and
reduction in thickness and weight, etc.
When the liquid-crystal cell is formed, one suitable functional
layer, or, two or more suitable functional layers may be provided
as occasion demands. Examples of such a functional layer include an
aligned film made of a rubbed film, etc., for aligning the liquid
crystal, a color filter for color display, and so on. Incidentally,
aligned films 61 and 62 are generally formed on transparent
electrodes 51 and 52 as shown in FIGS. 1 to 3. A color filter not
shown is generally provided between one of the cell substrates 41
and 42 and corresponding one of the transparent electrodes 51 and
52.
The liquid-crystal display panel may contain one suitable optical
layer or two or more suitable optical layers such as polarizers 21
and 22, phase retarders 31 and 32, a light diffusing layer 13, etc.
added to the liquid-crystal cell as shown in FIGS. 1 to 3. The
polarizers are provided for achievement of display using linearly
polarized light. The phase retarders are provided for improvement
of display quality by compensation, etc., for retardation due to
birefringence of liquid crystal. The light diffusing layer is
provided for enlargement of a display range by diffusion of display
light, uniformity of luminance by leveling of emission-line-like
light emission through slopes of the optical path changing sheet,
increase of the quantity of light incident on the optical path
changing sheet due to diffusion of transmission light in the
liquid-crystal display panel, etc.
A suitable material may be used as each of the polarizers without
any particular limitation. From the point of view of obtaining
good-contrast-ratio display due to incidence of highly linearly
polarized light, etc., an absorption type polarizing film made of a
drawn film having a dichromatic material such as iodine or
dichromatic dye adsorbed on a hydrophilic macromolecular film such
as a polyvinyl alcohol film, a partially formalized polyvinyl
alcohol film or a partially saponified ethylene-vinyl acetate
copolymer film may be preferably used. Or a film high in the degree
of polarization such as the absorption type polarizing film having
a transparent protective layer provided on one or each side of the
absorption type polarizing film may be preferably used.
A material excellent in transparency, mechanical strength, thermal
stability, moisture shielding characteristic, etc. is preferably
used for the formation of the transparent protective layer.
Examples of the material include: polymers such as acetate resin,
polyester resin, polyether-sulfone resin, polycarbonate resin,
polyamide resin, polyimide resin, polyolefin resin, acrylic resin,
polyether resin, polyvinyl chloride resin, polystyrene resin,
norbornene resin, and flurocarbon resin; heat-curable or
ultraviolet-curable resins such as acrylic resin, urethane resin,
acrylic urethane resin, epoxy resin, silicone resin, etc.; and so
on. The transparent protective layer may be bonded as a film by a
bonding method or may be applied as polymer liquid by a coating
method.
The polarizers to be used, especially the visual side polarizer may
be subjected to non-glare treatment or anti-reflection treatment
for preventing viewing from being disturbed by surface reflection
of external light. Non-glare treatment can be made by the formation
of a surface as a fine irregular structure. In the non-glare
treatment, various methods may be used for forming a surface as a
fine prismatic structure. Examples of the methods include: a
surface roughening method such as a sandblasting method, an
embossing method, etc.; a method of mixing transparent particles
such as silica particles; and so on. Anti-reflection treatment can
be made by a method of forming a coherent vapor deposition film, or
the like. Alternatively, non-glare treatment or anti-reflection
treatment can be made by a method of bonding a film having a
surface structure of fine prismatic structures or having an
interference film, or the like. Incidentally, two polarizers may be
provided on both sides of the liquid-crystal cell as shown in FIGS.
1 to 3 or one polarizer may be provided on one side of the
liquid-crystal cell.
On the other hand, each of the phase retarders may be formed of a
suitable material. Examples of the suitable material include a
birefringence film obtained by drawing a film of a suitable polymer
as illustrated in the description of the transparent protective
layer by a suitable method such as monoaxial drawing or biaxial
drawing, an aligned film of a suitable liquid-crystal polymer such
as a nematic liquid-crystal polymer or a discotic liquid-crystal
polymer, and an aligned layer of the aligned film supported by a
transparent base material. A material having a refractive index
controlled in a direction of thickness under the operation of heat
shrinkage force of a heat-shrinkable film may be also used. The
compensatory phase retarders 31 and 32 shown in FIGS. 1 to 3 are
generally disposed between the visual side polarizer 21 and the
liquid-crystal cell and/or between the back side polarizer 22 and
the liquid-crystal cell as occasion demands. A suitable material
may be used as each of the phase retarders in accordance with the
wavelength range, etc. Each of the phase retarders may be formed of
a laminate of two or more layers in order to control optical
characteristic such as retardation, etc.
The light diffusing layer can be provided by a suitable method
using a coating layer, a diffusing sheet, or the like, having a
similar surface structure of fine prismatic structures to that of
the non-glare layer. The light diffusing layer 13 shown in FIGS. 1
and 3 is formed of an adhesive layer containing transparent
particles. The light diffusing layer 13 serves also as a layer for
bonding the polarizer 22 and the phase retarder 32 to each other,
so that reduction in thickness is achieved. A suitable tackiness
agent may be used for the formation of the adhesive layer. The
tackiness agent contains, as a base polymer, a suitable polymer
such as a rubber polymer, an acrylic polymer, a vinyl-alkyl-ether
polymer, a silicone polymer, a polyester polymer, a polyurethane
polymer, a polyether polymer, a polyamide polymer, a styrene
polymer, etc.
Especially, a tackiness agent excellent in transparency, weather
resistance, heat resistance, etc. such as a tackiness agent
containing, as abase polymer, a polymer mainly containing alkyl
ether of acrylic acid or methacrylic acid is used preferably. As
the transparent particles mixed with the adhesive layer, there can
be used one or two members suitably selected from the group
consisting of inorganic particles of silica, alumina, titania,
zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide,
or the like, each of which has a mean particle size in a range of
from 0.5 to 20 .mu.m and which may be electrically conductive, and
organic particles of a crosslinked or non-crosslinked polymer, or
the like.
The illuminators disposed on side surfaces of the liquid-crystal
display panel are provided so that light to be utilized as light
for illuminating the reflection-transmission double type
liquid-crystal display device in a transmission (switched-on) mode
is made incident on the side surfaces of the liquid-crystal display
panel. Hence, reduction in thickness and weight of the
liquid-crystal display device can be achieved when the illuminators
are used in combination with the optical path changing sheet
disposed on the back side of the panel. A suitable illuminator can
be used as each of the illuminators. Examples of the illuminator
preferably used include a linear light source such as a (cold or
hot) cathode tube, a point light source such as a light-emitting
diode, an array of point light sources arranged in line or plane,
and a combination of a point light source and a linear light pipe
for converting the incident light from the point light source into
light of a linear light source through the linear light pipe.
One illuminator 91 may be disposed on one of side surfaces of the
liquid-crystal display panel L as shown in FIGS. 1 and 2 or
illuminators 91 and 93 may be disposed on two or more side surfaces
of the liquid-crystal display panel L as shown in FIG. 3. When
illuminators are disposed on a plurality of side surfaces, the
plurality of side surfaces may be provided as a combination of side
surfaces opposite to each other as shown in FIG. 3 or may be
provided as a combination of side surfaces crossing each other.
Further, the plurality of side surfaces may be provided as a
combination of three or more side surfaces by use of the
aforementioned combinations.
The illuminators make it possible to view the liquid-crystal
display device in a transmission mode in which the illuminator is
switched on. In the case where the liquid-crystal display device is
provided as a transmission-reflection double type liquid-crystal
display device, the illuminators can be switched on/off because
they are unnecessary to be switched on when the liquid-crystal
display device is viewed by external light in a reflection mode. A
suitable method may be used for switching on/off the illuminators.
Any one of background-art methods may be used. Incidentally, the
illuminators may be of a multicolor light emission type in which
the color of emitted light can be changed. Or different types of
illuminators may be provided so that multicolor light emission can
be made by the different types of illuminators.
As shown in FIGS. 1 to 3, each of the illuminators 91 and 93 may be
used in combination with a suitable assisting means such as a
reflector 92 or the like for enclosing the illuminator to lead
scattered light to side surfaces of the liquid-crystal display
panel L as occasion demands. A suitable reflection sheet such as a
resin sheet provided with a high-reflectance metal thin film, a
white sheet, a sheet of metal foil, etc. can be used as the
reflector. The reflector may be used also as a fixing means for
enclosing the illuminator by a method of bonding end portions of
the reflector to end portions of the cell substrate of the
liquid-crystal display panel, respectively.
The optical path changing sheet is disposed on the back side
(opposite to the visual side) of the liquid-crystal display panel
for the purposes as follows. That is, the optical path changing
sheet changes the optical path of the incident light or
transmission light .alpha. from the illuminator 91, which is
disposed on one of side surfaces of the liquid-crystal display
panel L as indicated by the arrow in FIG. 1, to the visual side of
the panel L through the optical path changing slopes A1 to thereby
utilize the light as illumination light (display light) in a
transmission mode. Further, the optical path changing sheet makes
the external light .beta. incident on the visual side of the
liquid-crystal display panel L in a switched-off state of the
illuminator 91 and makes the incident light be transmitted and
reflected by the flat surfaces A2 or A3 and the reflection layer 81
to thereby utilize the light as illumination light (display light)
in a reflection mode. For those purposes, the optical path changing
sheet 11 is provided with slopes A1 and flat surfaces A2 and A3 as
shown in FIGS. 1 to 3. The slopes A1 reflect the incident light a
from the illuminators 91 and 93 in a predetermined direction to
thereby change the optical path of the light. The flat surfaces A2
and A3 transmit incident external light .beta..
The optical path changing sheet is provided for fulfilling the
aforementioned reflection/transmission characteristic, especially
for obtaining illumination light excellent in frontal directivity
in both reflection and transmission modes. That is, the optical
path changing sheet is formed as an optical path changing sheet
having a plurality of optical path changing means A each
constituted by an optical path changing slope A1 facing a side
surface of arrangement of the illuminator, that is, facing an
incidence side surface at an inclination angle in a range of from
30 to 48 degrees with respect to a sheet plane, and flat surfaces
A2 and A3 inclined at an inclination angle of not larger than 10
degrees with respect to the sheet plane so that the projected area
of the flat surfaces A2 and A3 on the sheet plane is not smaller
than 10 times as large as the projected area of the optical path
changing slope A1 on the sheet plane. Especially, from the point of
view of reflection/transmission characteristic as described above,
it is preferable that an optical path changing sheet has a
plurality of optical path changing means A constituted by optical
path changing slopes A1 and formed into prismatic structures.
FIGS. 4A to 4G show examples of the optical path changing means A
having an optical path changing slope and flat surfaces and being
formed into prismatic structures as described above. In FIGS. 4A to
4E, each optical path changing means A is substantially shaped like
a triangle in section. In FIGS. 4F and 4G, each optical path
changing means A is substantially shaped like a rectangle in
section. In FIG. 4A, each optical path changing means A has an
isosceles triangle with two optical path changing slopes A1, and a
flat surface A3. In FIG. 4B, each optical path changing means A has
an optical path changing slope A1, a steep slope A2 having an
inclination angle larger than that of the slope A1 with respect to
the sheet plane, and a flat surfaces A3. In FIG. 4C, a plurality of
optical path changing means A are provided as a repetitive
structure in which the optical path changing means A are formed on
the whole surface of the sheet plane so as to be continued and
adjacent to one another, and each of the optical path changing
means A has an optical path changing slope A1 and a flat surface A2
having an inclination angle smaller than that of the slope A1 with
respect to the sheet plane. In FIGS. 4D and 4E, the reflection
layer 81 is provided on the flat surfaces A3 shown in FIG. 4B or on
the flat surfaces A2 shown in FIG. 4C. In FIG. 4F, each optical
path changing means A is constituted by a convex portion
(protrusion). In FIG. 4G, each optical path changing means A is
constituted by a concave portion (groove).
Hence, each optical path changing means may be formed from a
concave or convex portion constituted by equal-side surfaces or
slopes having equal inclination angles as described above.
Alternatively, each optical path changing means may be formed of a
concave or convex portion constituted by a combination of an
optical path changing slope and a steep slope or a flat surface or
slopes different in inclination angle. The shape of each optical
path changing means may be determined suitably in accordance with
the number of incidence side surfaces and the position of each
incidence side surface. From the point of view of improving
mar-proofness to keep the slope function high, the optical path
changing means constituted by a concave portion is superior to each
optical path changing means constituted by a convex portion because
the optical path changing means constituted by a concave portion is
hardly damaged at its slopes.
From the point of view of changing the optical path with good
frontal directivity in a transmission mode, each of the optical
path changing slopes A1 is preferably provided so as to face a
corresponding incidence side surface. Hence, when illuminators are
disposed on two or more side surfaces of the liquid-crystal display
panel and two or more incidence surfaces are therefore provided, an
optical path changing sheet having optical path changing slopes A1
corresponding to the number and positions of the incidence side
surfaces is used preferably. Incidentally, when illuminators 91 and
93 are disposed on two opposite side surfaces of the liquid-crystal
display panel L as shown in FIG. 3, there is preferably used an
optical path changing sheet 11 having optical path changing slopes
A1 every two of which constitute an optical path changing means A
substantially shaped like an isosceles triangle in section as shown
in FIG. 4A, or an optical path changing sheet 11 having optical
path changing slopes A1 every two of which constitute an optical
path changing means A substantially shaped like a trapezoid in
section as shown in FIGS. 4F and 4G so that the ridgelines formed
by the optical changing slopes A1 are parallel to the incidence
side surfaces respectively.
When illuminators are disposed on two adjacent cross side surfaces
of the liquid-crystal display panel, there is preferably used an
optical path changing sheet 11 having optical path changing slopes
A1 corresponding to the side surfaces respectively so that the
ridgelines formed by the optical path changing slopes A1 are
parallel to the two cross side surfaces respectively. When
illuminators are disposed on three or more side surfaces inclusive
of opposite side surfaces and adjacent cross side surfaces, there
is preferably used an optical path changing sheet 11 having optical
path changing slopes A1 constituted by a combination of the
aforementioned slopes.
The aforementioned optical path changing slopes A1 have a role of
reflecting the light incident on the slopes A1 among the light
incident on the incidence side surface from the illuminator or the
transmission light from the illuminator to thereby change the
optical path of the light and supply the light to the visual side
of the liquid-crystal display panel. In this case, when the
inclination angle of each of the optical path changing slopes A1
with respect to the sheet plane is selected to be in a range of
from 30 to 48 degrees, the optical path of the light incident on
the side surface or the transmission light .alpha. from the
illuminator 91 can be changed with good frontal directivity as
indicated by the arrow of polygonal-line in FIG. 1 as to be
sufficiently perpendicular to the sheet plane so that illumination
light excellent in frontal directivity can be obtained efficiently.
If the inclination angle is smaller than 30 degrees, the optical
path of the reflected light is generally largely shifted by 30
degrees or more from the frontal direction. Accordingly, frontal
luminance in a transmission mode becomes poor because the reflected
light is difficult to be utilized for display effectively. If the
inclination angle is larger than 48 degrees, the condition for
total reflection of the light incident on the side surface or the
transmission light cannot be satisfied. Accordingly, efficiency of
utilization of the light incident on the side surface may run short
because the light leaking from the optical path changing slopes
increases.
From the point of view of optical path change excellent in frontal
directivity, suppression of leaking light, etc., and in
consideration of the condition for total reflection of light
transmitted in the liquid-crystal display panel on the basis of
refraction in accordance with Snell's law, the inclination angle of
each of the optical path changing slopes A1 is preferably in a
range of from 35 to 46 degrees, more preferably in a range of from
38 to 45 degrees, further preferably in a range of from 40 to 44
degrees. Incidentally, the condition for total reflection by a
glass plate is generally 42 degrees. In this case, light incident
on the side surface is made incident on the optical path changing
slopes while transmitted in a condition that the incident light is
condensed in a range of .+-.42 degrees.
On the other hand, in the optical path changing sheet 11
functioning as a portion of incidence of external light and as a
portion of transmission of the incident light reflected by the
reflection layer 81 to enable display in a reflection mode by using
external light in a switched-off state of the illuminator, the
inclination angle of each of flat surfaces A2, A3, etc. is
preferably selected to be not larger than 10 degrees with respect
to the sheet plane from the point of view of reflecting incident
external light in the frontal direction as much as possible. The
preferable flat surfaces from the point of view of frontal
directivity of the reflected light are flat surfaces A2 inclined at
an inclination angle of not larger than 8 degrees, especially not
larger than 5 degrees, more especially not larger than 3 degrees;
or flat surfaces A3 inclined at an inclination angle of about 0
degrees.
In the aforementioned case, especially when the optical path
changing means A are formed as a repetitive structure in which the
optical path changing means A are continued and adjacent to one
another and each of the optical path changing means A has an
optical path changing slope A1 and a flat surface A2 as shown in
FIGS. 4C and 4E, the angle difference between inclination angles of
the flat surfaces A2 with respect to the sheet plane on the whole
of the optical path changing sheet is selected, preferably, to be
not larger than 5 degrees, more preferably not larger than 4
degrees, further preferably not larger than 3 degrees, and the
difference between inclination angles of adjacent flat surfaces A2
is selected preferably to be not larger than 1 degree, more
preferably not larger than 0.3 degrees, further preferably not
larger than 0.1 degrees. This arrangement is for the purpose of
preventing the optimum viewing direction of the liquid-crystal
display device in a reflection mode, especially the optimum viewing
direction in a direction near the frontal direction, from changing
largely due to reflection by the flat surfaces A2, particularly
from changing largely in between adjacent flat surfaces.
To achieve bright display in a reflection mode on the basis of
improvement in efficiency of incidence of external light and in
efficiency of transmission of the light reflected by the reflection
layer, the flat surfaces are formed so that the projected area of
the flat surfaces on the sheet plane is selected to be not smaller
than 10 times, particularly not smaller than 12 times, more
particularly not smaller than 15 times as large as the projected
area of the optical path changing slopes A1 on the sheet plane.
Hence, in the case of a plurality of optical path changing means A
each containing a steep slope A2 not functioning as the
aforementioned flat surface as illustrated in FIGS. 4B and 4D, it
is preferable that the angle of each of the steep slopes A2 is
selected to be not smaller than 35 degrees, particularly not
smaller than 50 degrees, more particularly not smaller than 60
degrees so that the width of each of the flat surfaces A3 can be
widened. The flat surfaces each having the aforementioned
inclination angle are favorable in terms of reflecting backward the
light incident on the incidence side surface and transmitting
efficiently the reflected light toward the opposite surface side to
thereby emit light as uniformly as possible on the whole surface of
the liquid-crystal display in a transmission mode.
As illustrated in FIGS. 5, 6 and 7, the optical path changing means
A having optical path changing slopes and flat surfaces are
generally formed as a repetitive structure for the purpose of
reducing the thickness of the optical path changing sheet so that
the ridgelines of the optical path changing means A are parallel to
or inclined to the incidence side surface of the liquid-crystal
display panel L on which the illuminator 91 is disposed. In this
case, the optical path changing means A may be formed so as to be
continued from one end to the other end of the optical path
changing sheet as shown in FIGS. 5 and 6 or may be formed
intermittently and discontinuously as shown in FIG. 7. When the
optical path changing means A are formed discontinuously, it is
preferable, from the point of view of efficiency of incidence of
transmission light, efficiency of changing the optical path, etc.,
that the length of each prismatic structure made of a groove or a
protrusion in a direction of the incidence side surface is selected
to be not smaller than 5 times as large as the depth or height
thereof. Further, from the point of view of uniform light emission
on the display screen of the panel, the length is selected
preferably to be not larger than 500 .mu.m, more preferably in a
range of from 10 to 480 .mu.m, further preferably in a range of
from 50 to 450 .mu.m.
The sectional shape of the plurality of optical path changing means
A and the repetition pitch of the optical path changing slopes A1
defined by the sectional shape of the means A are not particularly
limited. They can be determined suitably in accordance with the
uniformity of light emission on the display screen of the panel,
etc., both in a transmission mode and in a reflection mode which
uses external light because the optical path changing slopes A1 are
factors for determining luminance in a transmission (switched-on)
mode. Hence, the quantity of light which optical path is changed
can be controlled on the basis of the distribution density of the
optical path changing means A.
Therefore, the inclination angles, the shapes, or the like, of the
slopes A1 or A2 may be equal on the whole surface of the sheet or
may be changed so that the inclination angle, the shape, or the
like, of the optical path changing means A is enlarged as the
optical path changing means goes farther from the incidence side
surface, as shown in FIG. 8, for the purpose of coping with
absorption loss and attenuation of transmission light due to the
optical path changing and therefore making light emission on the
display screen of the panel uniform. The plurality of optical path
changing means A may be disposed at regular intervals of a
predetermined pitch as shown in FIG. 8. Alternatively, as shown in
FIG. 9, the plurality of optical path changing means A may be
disposed at irregular intervals so that the pitch is narrowed as
the optical path changing means A goes farther from the incidence
side surface to thereby make the distribution density of the
optical path changing means A high. Alternatively, the pitch may be
provided as a random pitch so that light emission on the display
screen of the panel can be made uniform. In FIGS. 8 and 9, the
arrow shows the direction of transmission of light incident on the
incidence side surface.
In a reflection mode, unnatural display may be caused by shortage
of transmission of display light if the optical path changing
slopes A1 overlap pixels of the liquid-crystal cell. It is
preferable from the point of view of preventing the unnatural
display, etc., that the overlap area is reduced as much as possible
to thereby keep sufficient light transmittance through the flat
surfaces A2 or A3. From this point of view and in consideration
that the pixel pitch of the liquid-crystal cell is generally in a
range of from 100 to 300 .mu.m, each of the optical path changing
slopes A1 is selected preferably to be not larger than 40 .mu.m,
more preferably in a range of from 3 to 20 .mu.m, further
preferably in a range of from 5 to 15 .mu.m in terms of the
projected width thereof on the sheet plane. The aforementioned
projected width is also preferable from the point of view of
preventing display quality from being lowered because of
diffraction in consideration that the coherent length of a
fluorescent tube is generally set to about 20 .mu.m.
It is preferable from the aforementioned point of view that the
distance between adjacent ones of the optical path changing slopes
A1 is large. As described above, however, the optical path changing
slopes A1 also serve as a functional portion for substantially
generating illumination light by changing the optical path of light
incident on the side surface in a transmission mode. Hence, if the
distance is too large, illumination in a switched-on mode becomes
so sparse that display may be unnatural. In consideration of these
facts, the repetition pitch of the optical path changing slopes A1
is selected preferably to be not larger than 5 mm, more preferably
in a range of from 20 .mu.m to 3 mm, further preferably in a range
of from 50 .mu.m to 2 mm.
When the optical path changing means are constituted by a
repetitive prismatic structures, moire may occur because of
interference between the optical path changing means and the pixels
of the liquid-crystal cell. Although prevention of moire can be
made by adjustment of the pitch of the prismatic structures in the
repetitive structure, the pitch of the prismatic structures in the
repetitive structure is limited to the aforementioned preferable
range. Hence, measures against the case where moire occurs even the
pitch is in the aforementioned range become the problem to be
solved. In the present invention, it is preferable to use a method
in which the ridgelines of the prismatic structures are formed to
be inclined with respect to the incidence side surface so that the
prismatic structures in the repetitive structure can be arranged to
cross the pixels to thereby prevent moire. On this occasion, if the
inclination angle to the incidence side surface is too large,
deflection occurs in reflection by the optical path changing slopes
A1. As a result, large deviation occurs in the direction of
changing the optical path. This large deviation is apt to cause
lowering of display quality. Therefore, the inclination angle of
the ridgelines with respect to the incidence side surface is
selected preferably to be in a range of .+-.30 degrees, more
preferably in a range of .+-.25 degrees. Incidentally, the symbol
".+-." means the direction of inclination of the ridgelines with
the incidence side surface as a reference. If the resolution of the
liquid-crystal cell is so low that moire never occurs or if moire
is negligible, it is preferable that the ridgelines are arranged to
be as parallel with the incidence side surface as possible.
The optical path changing sheet may be formed from a suitable
material exhibiting transparency in accordance with the wavelength
range of the illuminator. Incidentally, examples of the material
used in a visible light range include polymers or curable resins as
illustrated in the description of the transparent protective layer,
glass, or the like. An optical path changing sheet made from a
material exhibiting no birefringence or little birefringence is
used preferably. From the point of view of suppressing the loss of
the quantity of the light which is enclosed by the panel because of
interface reflection so as not to be allowed to exit from the
panel; and therefore efficiently supplying the light, which is the
incident on the side surface or the transmission light of the
incident light, to the optical path changing sheet, especially to
the optical path changing slopes A1; the optical path changing
sheet is preferably formed from a material in which the refractive
index difference between the optical path changing sheet and the
nearest liquid-crystal cell substrate is not larger than 0.15,
especially not larger than 0.10, more especially not larger than
0.05 so that interface reflection is suppressed.
The optical path changing sheet can be formed by a suitable method
such as a cutting method. Examples of the production A method
preferable from the point of view of mass production include: a
method in which a thermoplastic resin is pressed against a mold
capable of forming a predetermined shape by heating to thereby
transfer the shape; a method in which a mold capable of forming a
predetermined shape is filled with a hot-melted thermoplastic resin
or a resin fluidized by heat or by a solvent; a method in which a
fluid resin polymerizable by heat, by ultraviolet rays or by radial
rays is polymerized in the condition that the fluid resin is cast
in a mold capable of forming a predetermined shape, or in the
condition that a mold capable of forming a predetermined shape is
filled with the fluid resin; and so on. The thickness of the
optical path changing sheet can be determined suitably. From the
point of view of reduction in thickness, etc., generally, the
thickness of the optical path changing sheet is selected preferably
to be not larger than 300 .mu.m, more preferably in a range of from
5 to 200 .mu.m, further preferably in a range of from 10 to 100
.mu.m. Incidentally, the optical path changing sheet may be also
formed by a method of adding a plurality of optical path changing
means made of the same kind of material or different kinds of
materials to a resin sheet.
From the point of view of improvement in efficiency of transmission
light supply to the optical path changing slopes A1 by suppression
of interface reflection, improvement in efficiency of incidence of
external light on the optical path changing sheet, improvement in
luminance by effective utilization of the light incident on the
side surface and external light, etc., it is preferable that the
optical path changing sheet is bonded onto the back side (opposite
to the visual side) of the liquid-crystal display panel L as shown
in FIGS. 1 to 3 through an adhesive layer 12 in which the
refractive index difference between the adhesive layer and the
nearest liquid-crystal cell substrate is not larger than 0.2,
particularly not larger than 0.1, more particularly not larger than
0.05. On this occasion, as shown in FIGS. 1 to 3, it is preferable,
from the point of view of efficiency of utilization of transmission
light and external light, etc., that the optical path changing
sheet is disposed so that the surface on which a plurality of
optical path changing means A are formed is located on the outer
surface (on the back side which is opposite to the visual side).
The adhesive layer 12 may be of a light diffusion type similarly to
the adhesive layer 13 on the visual side.
As shown in FIGS. 1 to 3, a reflection layer 81 may be disposed on
the outer surface, that is, on the backside (opposite to the visual
side) of the optical path changing sheet 11. As described above,
the reflection layer is provided for enabling viewing in a
reflection mode of the liquid-crystal display device. The
reflection layer is also effective in improving light utilizing
efficiency in a transmission mode by reflecting and inverting the
light leaking from the optical path changing sheet to thereby make
the light incident on the optical path changing sheet again. The
reflection layer may be merely put on the outer surface of the
optical path changing sheet 11 as shown in FIG. 3 or may be bonded
to the optical path changing sheet 11 by an adhering method, a
vapor deposition method, or the like, as shown in FIGS. 1 and 2.
When the reflection layer 81 is bonded to the
optical-path-changing-means-forming surface of the optical path
changing sheet 11 as shown in FIGS. 1 and 2, the reflecting effect
can be improved to thereby prevent light leakage approximately
perfectly and improve viewing angle characteristic and luminance
more greatly.
Therefore, the reflection layer can be formed of a suitable
material such as a white sheet, etc., in accordance with the
background art. Especially, as a preferable example, a
high-reflectance reflection layer is constituted by: a coating
layer containing powder of a high-reflectance metal such as
aluminum, silver, gold, copper or chromium in a binder resin, or
alloy powder of such a high-reflectance metal; a layer of the
above-mentioned metal or a dielectric multilayer film deposited by
a suitable thin-film forming method such as a vacuum vapor
deposition method, a sputtering method, or the like; a reflection
sheet having the coating layer or the deposited layer supported by
a base material made of a film, or the like; a sheet of metal foil;
and so on.
In the present invention, from the point of view of improvement of
visibility both in a reflection mode and in a transmission mode,
especially improvement of visibility in a reflection mode by
improving frontal directivity of light, it is preferable that the
light reflected by the reflection layer is diffused and made
incident on the liquid-crystal cell. Such diffusion of the
reflected light can be performed by a method as follows. That is,
examples of the method include: a method of providing a light
diffusion type adhesive layer for bonding the optical path changing
sheet to the liquid-crystal display panel; a method of providing a
light diffusion type optical path changing sheet or a light
diffusion type reflection layer, and a method using these methods
in combination. Specifically, an optical path changing sheet having
a reflection layer made of a high-reflectance metal thin film may
be bonded onto the optical path changing slope-forming surface
through a light diffusion type adhesive layer. Alternatively, a
reflection layer made of a high-reflectance metal thin film maybe
provided on the optical-path-changing-slope-forming surface in an
optical path changing sheet or a light diffusion type optical path
changing sheet having the optical path changing slope-forming
surface roughened. Alternatively, a light diffusion type reflection
layer 81 may be provided as shown in FIG. 1.
The light diffusion type reflection layer may be formed by a
suitable method. Examples of the suitable method include: a method
of providing a reflection layer on a film base material having a
surface structure of fine prismatic structures by a suitable method
using a surface roughening method using sandblasting, matting, or
the like, or by a particle adding method so that the fine prismatic
structure of the film base material is reflected in the reflection
layer; and a method of providing a light diffusing layer containing
air bubbles or particles on the optical-path-changing-sheet-side
surface of the reflection layer; and so on.
The reflection layer having such a fine prismatic structure in
which the fine prismatic surface structure of the film base
material is reflected may be formed by a suitable method of
providing a metal on the surface of the film base material.
Examples of the suitable method include: a vapor deposition method
such as a vacuum vapor deposition method, an ion-plating method or
a sputtering method; a plating method; and so on. In this case, an
optical path changing sheet as described above may be used also as
the film base material. From the point of view of obtaining good
visibility both in a reflection mode and in a transmission mode on
the basis of suppression of scattering in a transmission mode, the
average inclination angle of the reflection layer in the fine
prismatic structure is selected preferably to be not larger than 15
degrees, more preferably in a range of from 4 to 12 degrees,
further preferably in a range of from 5 to 10 degrees.
Incidentally, in the case of a light diffusion type reflection
layer with a fine prismatic structure, there is also an advantage
in that the occurrence of Newton rings due to adhesion can be
prevented and visibility can be therefore improved.
In the liquid-crystal display device according to the present
invention, a great part of the light incident on the incident side
surface is transmitted backward through reflection in accordance
with the law of refraction through the upper and lower cell
substrates on the basis of thickness proportion of respective
layers in the liquid-crystal display panel. While the light emit
(leakage) from the surface of the panel is prevented and while
total reflection at the interface between the optical path changing
sheet 11 having the adjusted refractive index and the adhesive
layer 12 is suppressed, the optical path of the light incident on
the optical path changing slopes A1 of the optical path changing
sheet is efficiently changed to the viewing direction, that is, to
the frontal direction. The other part of the light is transmitted
backward by total reflection and made incident on the optical path
changing slopes A1 in the rear surface. The optical path of the
other part of the light is efficiently changed to the viewing
direction. Hence, display excellent in uniformity of brightness on
the whole surface of the panel display screen can be achieved in a
transmission mode. Moreover, display excellent in uniformity of
brightness on the whole surface of the panel display screen can be
achieved in a reflection mode similarly to the background-art
reflection exclusive type liquid-crystal display device. Hence, a
reflection-transmission double type liquid-crystal display device
which is bright, easy to view and excellent in display quality can
be formed because the light from the illuminator and external light
can be utilized efficiently.
Incidentally, in the present invention, optical devices or parts
such as an optical path changing sheet, a liquid-crystal cell, a
polarizer, a phase retarder, etc. for forming the liquid-crystal
display device may be wholly or partially integrally
laminated/fixed onto one another or may be disposed separably. From
the point of view of prevention of lowering of contrast by
suppressing the interface reflection, etc., it is preferable that
such optical devices or parts are fixed onto one another. A
suitable transparent adhesive agent such as a tackiness agent can
be used for the close fixing process. The transparent adhesive
layer may contain the transparent particles as described above so
that the transparent adhesive layer can exhibit a diffusing
function. The optical devices or parts, especially the visual side
of the optical devices or parts may be formed to have
ultraviolet-ray absorbing power by a method of treatment with an
ultraviolet-ray absorbent such as a salicylic ester compound, a
benzophenone compound, a benzotriazole compound, a cyanoacrylate
compound, a nickel complex salt compound, etc.
EXAMPLE 1
An acrylic ultraviolet-curable resin (ARONIX LTV-3701 made by
TOAGOUSEI Co., Ltd.) was dropped by a dropper so that a mold which
was processed into a predetermined shape in advance was filled with
the acrylic ultraviolet-curable resin. A triacetylcellulose (TAC)
film (having a saponified surface) 80 .mu.m thick was quietly set
on the acrylic ultraviolet-curable resin and then bonded to the
acrylic ultraviolet-curable resin by a rubber roller so that a
surplus of the resin and air bubbles were removed. Then, the
acrylic ultraviolet-curable resin was irradiated with ultraviolet
rays by a metal halide lamp so that the resin was hardened. Then,
the resin was released from the mold and cut into a predetermined
size. Thus, an optical path changing sheet was obtained to have an
optical path changing means layer with a refractive index of 1.533
formed on the TCA film with a refractive index of 1.485. An
adhesive layer having a refractive index of 1.47 was bonded onto a
surface of the optical path changing sheet in which no optical path
changing means was provided.
The optical path changing sheet was 40 mm wide and 30 mm deep. The
optical path changing sheet had prism-like concave portions which
were disposed continuously at intervals of a pitch of 210 .mu.m and
which formed ridgelines inclined at an angle of 23 degrees with
respect to the widthwise direction (FIG. 4C). Each of the
prism-like concave portions had an optical path changing slope A1,
and a flat surface A2. The inclination angle of each of the optical
path changing slopes A1 varied in a range of from 42.5 to 43
degrees. The inclination angle of each of the flat surfaces A2
varied in a range of from 1.8 to 3.5 degrees. The difference
between the inclination angles of adjacent ones of the flat
surfaces A2 was not larger than 0.1 degrees. The projected width of
each of the optical path changing slopes A1 on the sheet plane was
in a range of from 10 to 16 .mu.m. The ratio of the projected area
of the flat surfaces A2 on the sheet plane to the projected area of
the optical path changing slopes A1 on the sheet plane was not
smaller than 12.
Then, a cold-cathode tube was disposed on one of side surfaces of a
normally white transmission type TN liquid-crystal display panel
which was already available on the market. The cold-cathode tube
was enclosed by a reflector made of a silver-vapor-deposited
reflection sheet. Opposite end portions of the reflector were
bonded to upper and lower surfaces of the panel so that the
cold-cathode tube was fixed. Then, a light diffusing film including
a TAC film and a resin-fine-particle-containing adhesive layer
provided on the TAC film was bonded to a polarizer on the back side
(opposite to the visual side) of the liquid-crystal display panel.
The aforementioned optical path changing sheet was bonded onto the
light diffusing film so that the optical path changing slopes faced
the cold-cathode tube. The panel was disposed on a light diffusion
type reflection sheet made of a silver-vapor-deposited film having
a surface structure of fine prismatic structures so that the
optical path changing sheet was positioned on the back side which
was opposite to the visual side of the panel. Thus, a
reflection-transmission double type liquid-crystal display device
was obtained. Incidentally, the refractive index of the cell
substrate near the optical path changing sheet in the
liquid-crystal display panel was 1.485.
EXAMPLE 2
A reflection-transmission double type liquid-crystal display device
was obtained in the same manner as that in Example 1 except that
the optical path changing sheet was replaced by an optical path
changing sheet having a plurality of optical path changing means
(FIG. 4B) each of which had an optical path changing slope A1
inclined at an inclination angle of about 42 degrees, a steep slope
A2 making a vertical angle of 70 degrees with respect to the
optical path changing slope A1, and a flat portion A3 having an
area of not smaller than 10 times as large as the total projected
area of the optical path changing slope A1 and the steep slope A2
on the sheet plane.
EXAMPLE 3
A reflection-transmission double type liquid-crystal display device
was obtained in the same manner as that in Example 1 except that
the optical path changing sheet was replaced by an optical path
changing sheet (FIGS. 7 and 9). The sheet had a plurality of
optical path changing means (FIG. 4B) each of which had a length of
80 .mu.m, and each of which had an optical path changing slope A1
inclined at an inclination angle of about 42 degrees with a
projected width of 10 .mu.m on the sheet plane, and a steep slope
A2 inclined at an inclination angle of about 55 degrees. In the
sheet, the longitudinal direction of each optical path changing
means was parallel to the incidence side surface, and the plurality
of optical path changing means were disposed gradually with a
higher density as the optical path changing means went farther from
the incidence side surface in the depthwise direction.
Incidentally, the area of the flat portions A3 was not smaller than
10 times as large as the total projected area of the optical path
changing slopes A1 and the steep surfaces A2 on the sheet
plane.
EXAMPLE 4
A reflection-transmission double type liquid-crystal display device
was obtained in the same manner as that in Example 1 except that
the optical path changing sheet was replaced by an optical path
changing sheet (FIG. 7). The sheet had a plurality of optical path
changing means (FIG. 4A) each having a length of 80 .mu.m, and each
having an isosceles triangle with two optical path changing slopes
A1 which were inclined at an inclination angle of about 42 degrees
and each of which had a projected width of 10 .mu.m on the sheet
plane. In the sheet, the longitudinal direction of each optical
path changing means was parallel to the Incidence side surface and
the plurality of optical path changing means were disposed at
random so that the optical path changing means were gradually dense
as the optical path changing means went farther from the incidence
side surface toward the center portion in the depth wise direction
and so that cold-cathode tubes were disposed on two opposite side
surfaces of the optical path changing sheet. Incidentally, the area
of the flat portions A3 was not smaller than 10 times as large as
the total projected area of the optical path changing slopes A1 on
the sheet plane.
EXAMPLE 5
A surface of a mold portion for forming flat portions A2 of an
optical path changing sheet was roughened by sandblasting while the
other portion was masked. A silver-vapor-deposited film was
directly provided on the roughened surface portion to thereby form
a reflection layer. Thus, an optical path changing sheet (FIG. 4E)
was obtained. A reflection-transmission double type liquid-crystal
display device was obtained in the same manner as that in Example 1
except that the optical path changing sheet was used while the
light diffusion type reflection sheet was omitted.
EXAMPLE 6
A surface of a mold portion for forming flat portions A3 of an
optical path changing sheet was roughened by sandblasting while the
other portion was masked. A silver-vapor-deposited film was
directly provided on the roughened surface portion to thereby form
a reflection layer. Thus, an optical path changing sheet (FIG. 4D)
was obtained. A reflection-transmission double type liquid-crystal
display device was obtained in the same manner as that in Example 2
except that the optical path changing sheet was used while the
light diffusion type reflection sheet was omitted.
EXAMPLE 7
A reflection-transmission double type liquid-crystal display device
was obtained in the same manner as that in Example 2 except that
styrene fine particles with a refractive index of 1.59 were mixed
with the adhesive layer to form a light diffusion type adhesive
layer and except that the light diffusion type reflection sheet was
replaced by a reflection layer prepared by directly providing a
silver-vapor-deposited film on a surface of the optical path
changing sheet on which the optical path changing means were
formed.
COMPARATIVE EXAMPLE 1
A reflection-transmission double type liquid-crystal display device
was obtained in the same manner as that in Example 1 except that
the optical path changing sheet was replaced by a scattering sheet
subjected to sandblasting. Incidentally, the scattering sheet was
disposed so that the roughened surface was positioned on the back
side (opposite to the visual side).
COMPARATIVE EXAMPLE 2
A reflection-transmission double type liquid-crystal display device
was obtained in the same manner as that in Example 1 except that
the optical path changing sheet was replaced by an optical path
changing sheet having a plurality of optical path changing means
(FIG. 4B) each of which had an optical path changing slope A1
inclined at an inclination angle of about 25 degrees, a steep slope
A2 making a vertical angle of 70 degrees with respect to the
optical path changing slope A1, and a flat portion A3 having an
area of not smaller than 10 times as large as the total projected
area of the optical path changing slope A1 and the steep slope A2
on the sheet plane.
COMPARATIVE EXAMPLE 3
A reflection-transmission double type liquid-crystal display device
was obtained in the same manner as that in Example 1 except that
the optical path changing sheet was replaced by an optical path
changing sheet having a plurality of optical path changing means
(FIG. 4B) which were disposed at intervals of a pitch of 10 .mu.m,
and each of which had an optical path changing slope A1 inclined at
an inclination angle of about 42 degrees with a projected width of
from 18 to 27 .mu.m on the sheet plane, a steep slope A2 making a
vertical angle of 70 degrees with respect to the optical path
changing slope A1, and a flat portion A3 having an area of not
larger than 5 times as large as the total projected area of the
optical path changing slope A1 and the steep surface A2 on the
sheet plane.
COMPARATIVE EXAMPLE 4
A reflection-transmission double type liquid-crystal display device
was obtained in the same manner as that in Comparative Example 1
except that the light diffusion type reflection sheet was replaced
by a reflection layer prepared by directly providing a
silver-vapor-deposited film on the back side of a scattering
sheet.
COMPARATIVE EXAMPLE 5
A cold-cathode tube was disposed on one of side surfaces of a 1.2
mm-thick light pipe having an embossed rough surface on the back
side (opposite to the visual side). The cold-cathode tube was
enclosed by a reflector made of a silver-vapor-deposited reflection
sheet. Opposite end portions of the reflector were bonded to upper
and lower surfaces of the light pipe. The light pipe was disposed
on a light diffusion type reflection sheet made of a
silver-vapor-deposited film having a surface structure of fine
prismatic structures. A normally white reflection-transmission
double type TN liquid-crystal display panel which was already
available on the market was disposed on the light pipe through a
light diffusing plate. Thus, a reflection-transmission double type
liquid-crystal display device was obtained.
Evaluation Test
Frontal luminance in the center portion of the
reflection-transmission double type liquid-crystal display device
obtained in each of Examples and Comparative Examples was measured
in a transmission mode by a luminance meter (BM-7 made by TOPCON
Corp.) while the cold-cathode tube was switched on in the condition
that the liquid-crystal cell was supplied with no voltage. Further,
frontal luminance was also measured in a reflection mode in the
case where illumination was made by a ring-like illuminator so that
external light was incident at an angle of 30 degrees while the
cold-cathode tube was switched off in the same condition as
described above. Results of the measurement were shown in the
following Table.
Frontal Luminance (cd/m.sup.2) Reflection Mode Transmission Mode
Example 1 409 22 Example 2 432 23 Example 3 462 21 Example 4 382 38
Example 5 467 25 Example 6 512 24 Example 7 457 26 Comparative
Example 1 448 4 Comparative Example 2 422 9 Comparative Example 3
330 29 Comparative Example 4 531 3 Comparative Example 5 381 33
It is apparent from the Table that excellent frontal luminance was
achieved in a transmission mode in Examples 1 to 7 compared with
Comparative Examples 1, 2 and 4. These results in Comparative
Examples 1, 2 and 4 are caused by the exit light in a transmission
mode which exited in a direction reverse to the light source so as
to hardly contribute to display because of poor frontal luminance.
Particularly in Comparative Examples 1 and 4, exit light ran short
in all directions. In Comparative Example 3, light in the vicinity
of the light source was so intensive that uniformity of brightness
on the whole display screen was inferior as well as display in a
reflection mode was dark. On the other hand, in Example 4,
improvement of luminance by use of the two light sources was
remarkable. It is apparent that more brightness was obtained in
Example 4 in comparison with the side-lighting type light pipe in
Comparative Example 5. Incidentally, in the system using the
side-lighting type light pipe in Comparative Example 5, increase of
thickness due to the light pipe was remarkable, so that it was
difficult to reduce the thickness.
In each of Examples and Comparative Examples, good display quality
was obtained in a transmission mode because there was no problem on
visibility in the condition that a voltage was applied to the
liquid-crystal cell. In a reflection mode in Comparative Example 5,
display was seen as if it was in the deep and was not easy to view
because display was performed by the reflection surface through the
light pipe. On the other hand, the case where the light diffusing
sheet was removed in Example 2 was inferior in visibility but equal
in frontal luminance in a transmission mode to the case where the
light diffusing sheet was provided. In a reflection mode, there is
no particular problem except that slight stripes caused by the
optical path changing means were viewed. It is proved from the
above description that a reflection-transmission double type
liquid-crystal display device excellent in display quality can be
formed according to the present invention while increase in volume
and weight due to the light pipe is avoided so that reduction in
thickness and weight is achieved by a sheet method.
While the presently preferred embodiment of the present invention
has been shown and described, it is to be understood that the
disclosure is for the purpose of illustration and that various
changes and modification may be made without departing from the
scope of the invention as set forth in the appended claims.
* * * * *